• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.183-184
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• 2014

The multi-environment probability density function model has been applied to simulate the turbulent stratified premixed flames. The direct quadrature method of moments (DQMOM) has been adopted to solve the transport PDF equation due to its computational efficiency and robustness. Computations are made for the non-swirling turbulent stratified premixed flames including SWB1, SWB5 and SWB9. The numerical results obtained in this study are precisely compared with experimental data in terms of axial velocity, unconditional means and conditional means for scalar field including temperature and species mass fraction.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.690-700
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a circular cylinder were examined in a wind tunnel. In order to produce strong thermal stratifications, a compact heat exchanger type variable electric heater is employed. Linear temperature gradient of up to $250^{\circ}C/m$ can be well sustained. The velocity and temperature profiles in the cylinder wake with a strong thermal gradient of $200^{\circ}C/m$ were measured and the smoke wire flow visualization method was used to investigate the wake characteristics. It is found that the temperature field effects as an active contaminant, so that the mean velocity and temperature profiles can not sustain their symmetricity about the wake centerline when such a strong thermal gradient is superimposed. It is evident that the turbulent mixing in the upper half section is stronger than that of the lower half of the wake in a stably stratified flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.12
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• pp.3360-3371
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• 1995

Hydrodynamic characteristics of a stratified flow at a Y-junction were examined analytically. Gas is supplied through the main horizontal channel and liquid is introduced into the gas stream from the Y-shaped bottom branch. Analysis was performed with irrational flow and inviscid fluid assumptions. The Stokes' inverse transformation technique was adopted to convert the real x-y plane into the x-.psi. plane. The potential flow equation was solved numerically in the transformed (x-.psi.) plane and the interface profile, pressure distribution and the streamlines were obtained. The effects of the inlet conditions, injection angle and the gravity on the flow characteristics were also examined. To check the validity of the present method, the previous resultant the two-dimensional obtuse wedge flow was compared. The inverse transformation technique turned out to be also very useful to predict the hydrodynamic characteristics of a stratified flow with the pressure variation at a Y-shaped mixing junction.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.43-50
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• 2002

In the present study, reduction of harmful exhaust gas in a diesel engine using stratified injection system of dual fuel (diesel fuel and methanol) was tried. The nozzle and fuel injection pump of conventional injection system were remodeled to inject dual fuel in order from the same injector. The quantity of each fuel was controlled by micrometers, which were mounted at rack of injection pumps. The injection ratio of dual fuel was certificated by volumetric ratio in injection quantity test. Cylinder pressure and exhaust gas were measured and analyzed under various supply condition of duel fuel. We confirmed that combustion of dual fuel was performed successful1y by using modified injection system in a D.I. diesel. Soot and NOx are simultaneously reduced by stratified injection without large deterioration of thermal efficiency, but THC and CO are relatively increased.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.86-96
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• 2007

A direct-injection stratified-charge(DISC) engine has been considered as a promising alternative in spite of high unburned hydrocarbon emission levels during light load operation. In this paper investigation is made to characterize formation and combustion processes of stratified mixture charge in a simple constant volume combustion chamber. Both experimental and numerical analyses are performed for fluid and combustion characteristics with 3 different induction types for rich, homogeneous and lean mixture conditions. The commercial code FIRE is applied to the turbulent combustion process in terms of measured and calculated pressure traces and calculated distributions of mean temperature, OH radical and reaction rate. It turns out that the highest combustion rate occurs for the rich state condition at the spark ignition location due to existence of stoichiometric mixture and timing.

• Journal of the Society of Naval Architects of Korea
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• v.48 no.5
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• pp.414-420
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• 2011

Decades of studies of geophysical flow have unveiled that the flow downstream of obstacles in stratified flow consists of attached wake and strong gravity waves, or separated, fluctuating wake and persistent late wakes. Among unique and interesting characteristics of the stratified flow past obstacles is the generation of coherent vortex in the late wake far downstream of the object. Unlike in homogeneous fluid, the flow field downstream self-develops coherent vortex even after diminishing of the near wake, no matter how small the stratification is. This paper present a computational approach to simulate the generation of the coherent vortex structure in the late wake of a moving sphere submerged in weakly stratified fluid. The results are in consistent with several experimental observations and the vortex stretching mechanism is employed to explain the process of coherence.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2454-2462
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• 1994

The effects of thermal stratification on the flow of a stratified fluid past a heated circular cylinder were examined in a wind tunnel. Turbulent intensities, rms values of temperature and turbulent convective heat flux distributions in the heated cylinder wake with and without thermal stratification were measured by using a hot-wire and cold-wire combination probe. A phase averaging method was also used to estimated coherent motion in the near wake. It is found that the vertical turbulent motion in the stably stratified flow case dissipates faster than that of the neutral case, i.e., vertical growth of vortical structure is suppressed under the strongly stratified condition. The coherent motion of temperature makes a large contribution like velocity coherent motion. However, the coherent motions of temperature fluctuation become very different with the change of experimental conditions, though the velocity coherent motions are quite similar in all experimental conditions.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.103-106
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• 2002

This paper presents an effective numerical method for analyzing three-dimensional unsteady conjugate heat transfer problems of a curved pipe subjected to infernally thermal stratification. In the present numerical analyses, the thermally stratified flows in the pipe are simulated using the standard $k-{\varepsilon}$turbulent model and the unsteady conjugate heat transfer is treated numerically with a simple and convenient numerical technique. The unsteady conjugate heat transfer analysis method is implemented in a finite volume thermal-hydraulic computer code based on a non-staggered grid arrangement, SIMPLEC algorithm and higher-order bounded convection scheme. Numerical calculations have been performed far the two cases of thermally stratified pipe flows where the surging directions are opposite each other i.e. In-surge and out-surge. The results show that the present numerical analysis method is effective to solve the unsteady flow and conjugate heat transfer in a curved pipe subjected to infernally thermal stratification.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.940-947
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• 2005

An immersed boundary method for simulation of density-stratified flows has been developed and applied to computation of viscous flows past three different types of obstacle under table density stratification, namely laminar flows past a vertical barrier, a cosine hill, and a sphere, respectively. Density forcing is introduced on the body surface or inside the body. Significant changes in flow characteristics are observed depending on Fr. The numerical results are in good agreement with other authors' experimental and numerical results currently available, and shed light on computation of density-stratified flows in complex geometries.

• Journal of Power System Engineering
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• v.12 no.6
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• pp.64-69
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• 2008

The spatial fuel distribution of the stratified charge of a high pressure 6-hole injector was examined in a single cylinder optical direct injection spark ignition(DISI) engine. The effects of in-cylinder charge motion, and fuel injection pressure, and coolant temperature were investigated using a planar LIF(Laser Induced Fluorescence) technique. It was confirmed that the in-cylinder tumble flow played more effective role in the spatial fuel distribution of the stratified charge than the swirl flow during the compression stroke and the fuel distribution area increased due to the activation of the fuel vaporization by the increase of the coolant temperature. But, the increase of the fuel supplying pressure could not change the pattern of the fuel vapor distribution against the expectation.